U.S. patent application number 12/403989 was filed with the patent office on 2010-05-06 for molecular separators, concentrators, and detectors preparatory to sensor operation, and methods of minimizing false positives in sensor operations.
Invention is credited to Stephen J. Lukasik.
Application Number | 20100108580 12/403989 |
Document ID | / |
Family ID | 42130129 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100108580 |
Kind Code |
A1 |
Lukasik; Stephen J. |
May 6, 2010 |
Molecular Separators, Concentrators, and Detectors Preparatory to
Sensor Operation, and Methods of Minimizing False Positives in
Sensor Operations
Abstract
As an elegant solution for minimizing false positives returned
by a sensor tuned to an analyte molecule, filters constructed of
carbon nanotubes are positioned relative to the sensor to limit the
sensor to being exposed to molecules within a defined range of
sizes, with too-big molecules being excluded from reaching the
sensor by one filter, and too-small molecules being pumped out
through another, finer filter before the sensor is operated.
Inventors: |
Lukasik; Stephen J.; (Falls
Church, VA) |
Correspondence
Address: |
WHITHAM, CURTIS & CHRISTOFFERSON & COOK, P.C.
11491 SUNSET HILLS ROAD, SUITE 340
RESTON
VA
20190
US
|
Family ID: |
42130129 |
Appl. No.: |
12/403989 |
Filed: |
March 13, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61111048 |
Nov 4, 2008 |
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Current U.S.
Class: |
209/659 ;
707/E17.014; 715/764; 977/742; 977/845 |
Current CPC
Class: |
G01N 15/0272 20130101;
G01N 1/2205 20130101; G01N 1/40 20130101; G01N 2015/0038
20130101 |
Class at
Publication: |
209/659 ;
977/742; 977/845; 707/E17.014; 715/764 |
International
Class: |
B07C 5/04 20060101
B07C005/04 |
Claims
1. A method of sorting molecules by size, comprising: contacting at
least one nanotube having an inner diameter within a first
predetermined diameter range, with an initial sample of
various-sized molecules, to produce a screened sample.
2. The method of claim 1, further comprising contacting at least
one nanotube of an inner diameter within a second predetermined
diameter range which is not equal to the first predetermined
diameter range, to a screened sample to produce a size-sorted
sample.
3. The method of claim 2, wherein the at least one nanotube is
contained within a first screen comprising a plurality of nanotubes
having the first predetermined diameter range, and the at least one
nanotube having the second diameter is contained within a second
screen comprising a plurality of nanotubes having the second
predetermined diameter range.
4. A method of reducing an initial sample that contains
various-sized molecules to a subset of molecules of a predefined
size range, comprising: screening the initial sample to produce a
screened sample consisting of molecules of size smaller than a
maximum size; and requiring molecules of size smaller than a
minimum size to exit.
5. The method of claim 4, comprising producing a target sample
consisting of molecules having a size in the predefined size
range.
6. The method of claim 4, wherein the step of screening the initial
sample to produce a screened sample consisting of molecules of size
smaller than the maximum size includes applying a screen comprising
at least one nanotube having an inner diameter to exclude molecules
bigger than the maximum size.
7. The method of claim 4, wherein the step of requiring molecules
of size greater than the minimum size to exit includes applying a
screen comprising at least one nanotube having an inner diameter
that permits passage of molecules below the minimum size.
8. The method of claim 4, comprising passing the initial sample
through a screen comprising at least one nanotube having an inner
diameter to exclude molecules bigger than the maximum size,
followed by withdrawing, through a screen comprising at least one
nanotube having an inner diameter that permits passage of molecules
below the minimum size, a subset of molecules which are smaller
than the minimum size.
9. The method of claim 4, comprising a screening step of screening
an initial sample comprising at least one of an analyte molecule
and/or a molecule that evokes a false positive for the analyte
molecule.
10. The method of claim 4, comprising a screening step of screening
an initial sample comprising at least one pair of an analyte
molecule and/or a molecule that evokes a false positive for the
analyte molecule and is of a different size than the analyte
molecule.
11. A method, comprising: for an initial sample that contains
various-sized molecules, reducing the initial sample to a subset of
molecules of a predefined size range; bringing the subset of
molecules of the predefined size range into contact with at least
one sensor.
12. The method of claim 11, wherein the initial sample includes at
least one of an analyte molecule and/or a molecule that evokes a
false positive for the analyte molecule.
13. The method of claim 11, wherein the initial sample includes at
least one of an analyte molecule and/or a molecule that evokes a
false positive for the analyte molecule, and the reducing step
sorts the molecule that evokes a false positive.
14. The method of claim 11, wherein the initial sample includes a
set of molecules that are of a relatively large size, a set of
molecules that are of a relatively small size, and a target set of
molecules that are of a medium size which is the predefined size
range, and the reducing step reduces the initial sample to the
target set.
15. The method of claim 11, wherein the reducing step comprises a
step of screening-out too-big molecules and further comprises a
step of requiring too-small molecules to exit while screening-in
target-size molecules.
16. The method of claim 11, wherein the reducing step sorts at
least one molecule that would evoke a false positive and prevents
the molecule that would evoke the false positive from coming in
contact with the sensor.
17. A method of sorting, from an initial sample, a subset of
molecules that would activate false positives by a sensor which is
intended to detect a molecule or molecules, comprising: for the
sensor, identifying a size range of the analyte molecule or
molecules; sorting, from the initial sample, molecules outside the
identified size range of the analyte molecule or molecules.
18. The method of claim 17, wherein the sorting step comprises
applying at least a first screen comprising at least one nanotube
of an inner diameter that excludes too-big molecules, and further
comprises requiring too-small molecules to exit through at least
one nanotube of an inner diameter that permits passage of too-small
molecules.
19. The method of claim 18, wherein applying the first screen
includes applying a first screen that comprises an array of
nanotubes of an inner diameter that excludes too-big molecules, and
wherein requiring too-small molecules to exit includes requiring
too-small molecules to exit through a second screen that comprises
an array of nanotubes of an inner diameter that permits passage of
too-small molecules.
20. A method of processing an initial sample of a set of molecules
before contact with a sensor, comprising: directing the initial
sample of the set molecules into contact with an entry screen
leading into a container, the entry screen excluding from entry a
subset of molecules bigger than a molecular size range of molecules
wanted to be detected by the sensor; withdrawing from the container
a subset of molecules smaller than the molecular size range of
molecules wanted to be detected by the sensor.
21. The method of claim 20, wherein the initial sample includes at
least one molecule that would evoke a false-positive and after the
directing step and the withdrawing step, the molecule that would
evoke a false-positive is not within the container.
22. The method of claim 20, wherein the initial sample includes at
least one molecule that would evoke a false-positive and at least
one molecule that is intended to be detected by the sensor, and
after the directing step and the withdrawing step, the molecule
that would evoke a false-positive is not within the container and
the molecule that is intended to be detected by the sensor is
within the container.
23. A molecular separator comprising: a chamber comprising at least
a first screen and a second screen; the first screen comprising at
least one nanotube having an inner diameter that is a first
diameter or within a first range of diameters; the second screen
comprising at least one nanotube having an inner diameter that is a
second diameter or within a second range of diameters, which is
smaller than the first diameter or first range of diameters.
24. A method of assessing whether a sensor which has returned a
positive indication is false-alarming, comprising: when the sensor
has returned the positive indication for presence of a target
substance, operating a software-based query sequence in which a
series of yes/no queries are presented to a human user for yes/no
response, wherein each yes/no query tends to screen for whether the
target substance is actually present and being detected by the
sensor or whether instead the sensor is likely to be issuing a
false alarm.
25. An interactive interrogator system for detecting a target
substance, comprising: a sensor tuned to detect the target
substance; and a computer-based interrogator system that is
interactive with a user and that provides a series of interactive
queries that when answered by the user tend to screen for whether
the sensor is indeed detecting the target substance or rather is
likely to be detecting a non-target substance that would cause a
false alarm.
Description
RELATED APPLICATION
[0001] This application claims benefit of U.S. provisional
application Ser. No. 61/111,048 filed Nov. 4, 2008, the contents of
which are hereby incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to detection of
molecules, especially detection of molecules such as chemical
warfare agents, while reducing or avoiding false alarms.
BACKGROUND OF THE INVENTION
[0003] The sensing of analytes (such as chemical warfare agents,
etc.) with considerable sensitivity and specificity is a
requirement in many circumstances. Sensitivity is required to sense
analytes before their level reaches an undesired value. Specificity
is necessary to avoid false positives that would engender
unnecessary, costly, and potentially dangerous responses.
[0004] Chemical warfare agents are lethal compounds applied to
warfare have been developed over many years, some derived from
commercial compounds used to control destructive animals, insects,
and plants, others are toxic industrial chemicals, such as
chlorine, that also have been used in warfare. Still others are the
product of military research and development intended to produce
lethal agents of desired characteristics and effects.
[0005] The complexity and variety of chemical compounds, many only
slightly different in structure or chemical reactivity, make the
task challenging. False positive such as may originate from similar
compounds present in the sampled environment are a source of
concern.
[0006] For detecting certain molecules (such as chemical warfare
agents, etc.), there are various conventional sensors and detectors
that have been previously provided. However, these existing sensors
and detectors are not without flaws and shortcomings. For one,
there is wanted greater sensitivity, namely, the ability to detect
on the order of parts per trillion (ppt).
[0007] Significantly, current sensors and detectors tend to have a
false alarm (false positive) problem, namely, that the sensors and
detectors are triggered not just by what is wanted to be detected
but also triggered by "interferents." For example, in the case of
current sensors used by the chemical agent detector community,
benzene and toluene are potential interferents. These chemicals are
components of JP-8 and diesel fuel vapors and exhaust and
associated with a variety of burning materials and gunfire. False
alarm problems have been reported in the testing of currently used
fieldable chemical agent detectors in the presence of JP-8 and
diesel vapor and exhaust, as well as toluene. In these tests a
positive detection of either nerve or blister agents was registered
when neither of these chemical warfare agents was present.
[0008] Another example where sensitivity and specificity are needed
is in sensing compounds in the environment that are destructive to
the atmosphere and water and endanger the health of those exposed.
In other cases chemical sensing is important for the collection of
information about criminal and foreign military developments and
operations. In industrial operations, chemical sensing is necessary
to recognize when dangerous processes may be incompletely
contained, becoming uncontrolled, and/or potentially creating a
HAZMAT release.
[0009] There have not yet been provided, but are wanted, fieldable
devices with sensors that are both sufficiently sensitive and
versatile to provide for detection of a variety of important threat
agents and simultaneously discriminating of, or insensitive to,
interferents which would register false positives.
[0010] Also, there are needs for detecting toxic materials in water
samples. The safety of drinking water is of importance for military
deployments in combat zones. Domestically there is the treat of
terrorist attacks against water supply systems. A large concern is
the protection of populations against toxic chemicals that find
their way into drinking water, and into lakes, rivers, bays and
oceans where they harm animals and fish, and damage recreational
uses of such natural resources.
SUMMARY OF THE INVENTION
[0011] The present inventor has provided an elegant solution to the
difficult problem of how to minimize false positive readings in a
sensor, preferably while detecting the analyte or target molecules
(such as, e.g., chemical warfare agent, etc.) at the desired
sensitivity. The invention provides for preprocessing (such as,
e.g., inventive molecular separation) to be performed on a sample
to sort molecules from the sample before a sensor (such as, e.g., a
carbon nanotube bundle sensor) is operated on what remains of the
sample.
[0012] The operation of an inventive molecular separator
advantageously allows the molecular separator to function
simultaneously as a concentrator by drawing the sample through the
invention as a continuous flow, at each instant trapping the
desired molecules. This allows the analyte or analytes thereby
selected to accumulate in ever increasing numbers to a degree
proportional to the amount of time the sample flow is maintained.
Thus a variety of different sensors can be employed, varying in
their specific characteristics, and regardless of limits on the
minimum concentration of analyte needed for them to produce a
measurable electrical or other signal relatable to the
concentration of the intended analyte.
[0013] An objective of the present invention is to provide a
physical discriminant to reduce false positives, that of molecular
size. In some cases, such providing of a physical discriminant may
suffice to select only the desired compound from among the many
possibly present and exposed to a chemical sensor. In other cases,
additional a priori reasoning may be further performed to reduce or
eliminate potential interfering compounds (also known as
"interferents") based on external circumstances of the site where
the measurement is being made and other information available
remotely. In this invention, preferably a chemical sensor is
embedded in, and is a part of, a system created for some larger
purpose. In a significant class of applications, site-specific
information can be drawn upon to manage the sensor and interpret
the sensor's results.
[0014] The present invention recognizes and makes use of the fact
that the sizes of molecules of concern in many sensing applications
bear a close relationship to the sizes of atomic-level
nanostructures such as, e.g., those of carbon nanotubes.
Regularly-spaced columnar nanostructures can serve as molecular
size filters for external flows.
[0015] The invention in one aspect provides a method of sorting
molecules by size, comprising: contacting at least one nanotube
having an inner diameter within a first predetermined diameter
range, with an initial sample (such as, e.g., an initial sample
that is a gaseous sample; an initial sample of air; etc.) of
various-sized molecules, to produce a screened sample; such as,
e.g., inventive methods further comprising contacting at least one
nanotube of an inner diameter within a second predetermined
diameter range which is not equal to the first predetermined
diameter range, to a screened sample to produce a size-sorted
sample (such as, e.g., inventive methods wherein the at least one
nanotube is contained within a first screen comprising a plurality
of nanotubes having the first predetermined diameter range, and the
at least one nanotube having the second diameter is contained
within a second screen comprising a plurality of nanotubes having
the second predetermined diameter range).
[0016] In another aspect, the invention provides a method of
reducing an initial sample (such as, e.g., an initial sample that
is a gaseous sample) that contains various-sized molecules to a
subset of molecules of a predefined size range, comprising:
screening the initial sample to produce a screened sample
consisting of molecules of size smaller than a maximum size (such
as, e.g., a size D(max)); and requiring molecules of size smaller
than a minimum size (such as, e.g., a size D(min)) to exit, such
as, e.g., inventive methods comprising producing a target sample
consisting of molecules having a size in a range of D(min) to
D(max); inventive methods wherein the step of screening the initial
sample to produce a screened sample consisting of molecules of size
smaller than the maximum size (such as, e.g., D(max)) includes
applying a screen comprising at least one nanotube having an inner
diameter to exclude molecules bigger than the maximum size;
inventive methods wherein the step of requiring molecules of size
greater than the minimum size (such as, e.g., D(min)) to exit
includes applying a screen comprising at least one nanotube having
an inner diameter that permits passage of molecules below the
minimum size (such as, e.g., D(min)); inventive methods comprising
passing the initial sample through a screen comprising at least one
nanotube having an inner diameter to exclude molecules bigger than
the maximum size, followed by withdrawing, through a screen
comprising at least one nanotube having an inner diameter that
permits passage of molecules below the minimum size (such as, e.g.,
D(min)), a subset of molecules which are smaller than the minimum
size (such as, e.g., D(min)), such as, e.g. inventive methods
comprising performing the withdrawing step until the initial sample
has been transformed into a target sample consisting only of
molecules of the predefined size range; inventive methods
comprising screening an initial sample that is a gaseous sample;
inventive methods comprising a screening step of screening an
initial sample comprising at least one of an analyte molecule
and/or a molecule that evokes a false positive for the analyte
molecule; inventive methods comprising a screening step of
screening an initial sample comprising at least one pair of an
analyte molecule and/or a molecule that evokes a false positive for
the analyte molecule and is of a different size than the analyte
molecule; inventive methods practiced with a selective screening
structure that comprises: a first screen comprising at least one
nanotube having a first diameter; a second screen comprising at
least one nanotube having a second diameter which is smaller than
the first diameter, wherein the selective screening structure has a
size selectivity in a range between a minimum which equals about
the second diameter and a maximum which equals about the first
diameter; and other inventive methods.
[0017] The invention in another aspect provides a method,
comprising: for an initial sample (such as, e.g., an initial sample
that is a gaseous sample; an initial sample that includes at least
one of an analyte molecule and/or a molecule that evokes a false
positive for the analyte molecule; etc.) that contains
various-sized molecules, reducing the initial sample to a subset of
molecules of a predefined size range (such as, e.g., a reducing
step that sorts from the initial sample molecules which are outside
of a size range), and bringing the subset of molecules of the
predefined size range into contact with at least one sensor (such
as, e.g., a carbon nanotube bundle sensor; a sensor configured to
detect a chemical warfare agent; etc.), such as, e.g., inventive
methods wherein the initial sample includes at least one of an
analyte molecule and/or a molecule that evokes a false positive for
the analyte molecule; inventive methods wherein the initial sample
includes at least one of an analyte molecule and/or a molecule that
evokes a false positive for the analyte molecule, and the reducing
step sorts the molecule that evokes a false positive; inventive
methods wherein the initial sample includes a set of molecules that
are of a relatively large size, a set of molecules that are of a
relatively small size, and a target set of molecules that are of a
medium size which is the predefined size range, and the reducing
step reduces the initial sample to the target set; inventive
methods wherein the reducing step comprises a step of screening-out
too-big molecules and further comprises a step of requiring
too-small molecules to exit while screening-in target-size
molecules; inventive methods wherein the reducing step sorts at
least one molecule that would evoke a false positive and prevents
the molecule that would evoke the false positive from coming in
contact with the sensor; and other inventive methods.
[0018] In another aspect, the invention provides a method of
sorting, from an initial sample (such as, e.g., an initial sample
that is a gaseous sample), a subset of molecules that would
activate false positives by a sensor which is intended to detect a
molecule or molecules, comprising: for the sensor, identifying a
size range of the analyte molecule or molecules; sorting, from the
initial sample, molecules outside the identified size range of the
analyte molecule or molecules (such as, e.g., a sorting step that
comprises sorting molecules sized outside the size range of the
molecules intended to be sensed, before the sensor is applied; a
sorting step that comprises applying at least a first screen
comprising at least one nanotube of an inner diameter that excludes
too-big molecules, and further comprises requiring too-small
molecules to exit through at least one nanotube of an inner
diameter that permits passage of too-small molecules; and other
sorting steps), such as, e.g., inventive methods wherein applying
the first screen includes applying a first screen that comprises an
array of nanotubes of an inner diameter that excludes too-big
molecules, and wherein requiring too-small molecules to exit
includes requiring too-small molecules to exit through a second
screen that comprises an array of nanotubes of an inner diameter
that permits passage of too-small molecules; inventive methods
wherein the requiring too-small molecules to exit includes
operating a pump to create a flow of sample; and other inventive
methods.
[0019] For example, in an inventive method, when the class of
molecules to be sensed is that of nerve gases, the two filter sizes
would be such that molecules smaller than 1.320 nm are allowed to
enter the concentrator/sensor cell and molecules smaller than 0.727
nm are allowed to exit from the concentrator/sensor cell (with
these mentioned sizes corresponding, respectively, to the smallest
and largest sizes of nerve agents, GB (sarin) at the small end of
the selected range and the nerve agent VX at the large end of the
size range).
[0020] The invention in another aspect provides a method of
processing an initial sample (such as, e.g., an initial sample that
is a gaseous sample; an initial sample of air; etc.) of a set of
molecules before contact with a sensor, comprising: directing the
initial sample of the set molecules into contact with an entry
screen leading into a container, the entry screen excluding from
entry a subset of molecules bigger than a molecular size range of
molecules wanted to be detected by the sensor; withdrawing from the
container a subset of molecules smaller than the molecular size
range of molecules wanted to be detected by the sensor; such as,
e.g., inventive methods further comprising operating the sensor in
the container after the directing and withdrawing steps; inventive
methods wherein the initial sample includes at least one molecule
that would evoke a false-positive and after the directing step and
the withdrawing step, the molecule that would evoke a
false-positive is not within the container; inventive methods
wherein the initial sample includes at least one molecule that
would evoke a false-positive and at least one molecule that is
intended to be detected by the sensor, and after the directing step
and the withdrawing step, the molecule that would evoke a
false-positive is not within the container and the molecule that is
intended to be detected by the sensor is within the container; and
other inventive methods.
[0021] In another aspect the invention provides a molecular
separator comprising: a chamber comprising at least a first screen
and a second screen; the first screen comprising at least one
nanotube having an inner diameter that is a first diameter or
within a first range of diameters; the second screen comprising at
least one nanotube having an inner diameter that is a second
diameter or within a second range of diameters, which is smaller
than the first diameter or first range of diameters, such as, e.g.,
inventive molecular separators further comprising: an inlet valve
upstream of the chamber, a pump downstream of the chamber and an
exit portal through which molecules being separated-out as too
small exit the chamber; inventive molecular separators further
comprising a sensor (such as, e.g., a carbon nanotube bundle
sensor) disposed within or inserted into the chamber.
[0022] The invention in a further aspect provides a molecular
separator which separates molecules of a class defined by a
specified physical characteristic, such as, e.g., inventive
molecular separators that separate molecules that are in a gaseous
medium; inventive molecular separators that separate molecules
while distinguishing between molecules of other classes having
similar physical characteristics; inventive molecular separators
that distinguish between molecules having a specified parameter
greater than a D(min) and less than a D(max); inventive molecular
separators that include a sensor to produce a quantitative measure
of the concentration of the defined class of molecules in the range
of 1 ppm (part per million) to 1 ppt (part per trillion); inventive
molecular separators that can be used in both urban and rural
locations; inventive molecular separators that separate molecules
in a time period of less than 5 minutes; man-portable inventive
molecular separators; inventive molecular separators that can be
used in an automated or semi-automated mode of operation; and other
inventive molecular separators.
[0023] In another aspect the invention provides a method of
nanotube screening, comprising: vaporizing to convert analytes that
may be present in the sample as liquid phase droplets to reduce
such droplets to a vapor phase, and nanotube screening after
vaporizing.
[0024] The invention in another aspect provides a method of
assessing whether a sensor which has returned a positive indication
is false-alarming, comprising: when the sensor has returned the
positive indication for presence of a target substance, operating a
software-based query sequence in which a series of yes/no queries
are presented to a human user for yes/no response, wherein each
yes/no query tends to screen for whether the target substance is
actually present and being detected by the sensor or whether
instead the sensor could issue a false alarm.
[0025] In a further aspect the invention provides an interactive
interrogator system for detecting a target substance, comprising: a
sensor tuned to detect the target substance; and a computer-based
interrogator system that is interactive with a user and that
provides a series of interactive queries that when answered by the
user tend to screen for whether the sensor is indeed detecting the
target substance or could be detecting a non-target substance that
would cause a false alarm.
[0026] In another aspect, the invention provides a sensor-based
method of detecting an analyte (such as, e.g., tabun, soman,
cyclosarin, etc.), such as, e.g., inventive detecting methods that
comprise a step of subjecting an initial sample to a length
separation operation (such as, e.g., a subjecting to a length
separation step that sorts the initial sample into a size-sorted
sample including a mid-sized sample) in advance of a step of
operating the sensor (such as a sensor for an analyte) to take a
measurement (such as, e.g., a step of operating the sensor to take
a measurement of the mid-sized sample), followed by an
ambiguity-resolving step (such as, e.g., an ambiguity-resolving
step performed with respect to the mid-sized sample for which the
measurement was taken in the step of operating the sensor); and
other inventive sensor-based detecting methods that reduce false
alarms to a low level.
[0027] In another aspect, the invention provides for detecting
toxic materials in water samples.
BRIEF SUMMARY OF THE DRAWINGS
[0028] FIG. 1 is a cross-sectional schematic showing a detector
concept according to an embodiment of the invention in which the
inventive screens (a) are particularly noted.
[0029] FIG. 1A shows a cross-sectional schematic view of a nanotube
which is a preferred component of a screen in FIG. 1, with a
molecule small enough to pass through the nanotube also shown. As a
general state of affairs, analytes will be elongated rather than
spherical, as shown here schematically. However as a result of
their rapid kinetic motion and their frequent collisions with one
another and with the containing walls, they have both translational
and rotational kinetic energy. Thus an analyte, though it has an
elongated shape, is treated as a minimum-size circumscribing sphere
for addressing the relative size of an analyte and a nanotube
through which it travels.
[0030] FIG. 2 is a part of a table which may be used in practicing
the invention in an embodiment where a target molecule is tabun,
soman and/or cyclosarin; other than the rows for tabun, soman and
cyclosarin which are nerve agents, the two left-most columns in
FIG. 2 indicate interferents. In FIG. 2, the data for the nerve
agents and interferents include a standard chemical identification
number, molecular weight, melting point, boiling point, vapor
pressure, chemical formula, and the maximum diameter. In FIG. 2,
the rows have been sorted by maximum diameter and are shown in
increasing order of the diameter of a minimum circumscribing
sphere.
[0031] FIG. 3 is a block diagram that shows components used in
constructing a system 300 which is an inventive embodiment
including at least one cell 33.
[0032] FIG. 3A is a cross-sectional schematic of a cell 33 useable
in system 300 (FIG. 3). In FIG. 3A, numbering from FIG. 1 is
repeated where applicable.
[0033] FIG. 4 is a diagram of an inventive system 300 corresponding
to FIG. 3.
[0034] FIG. 5 is a flow chart for an inventive embodiment which
includes an ambiguity-resolving step 502.
[0035] FIG. 6 is a flow chart for an inventive reduced false-alarm,
sensor-based method of detecting an analyte which comprises a step
601 of subjecting an initial sample to length separation; a step
602 of operating a sensor to take a measurement; and an
ambiguity-resolving step 603.
[0036] FIG. 7 is a diagram for an inventive embodiment in which
water samples are processed.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0037] The invention may be appreciated with reference to the
figures, without the invention being limited thereto. Referring to
FIGS. 1-1A, a detector concept may be appreciated, according to
which may be constructed a system 100 useful for detecting an
analyte molecule (such as, e.g., an analyte molecule which is a
chemical warfare agent; etc.). "Analyte" is used herein according
to its ordinary meaning in the chemical arts and refers to a
substance or chemical constituent which is the subject of an
analysis. An analyte substance might also in the literature be
called a target substance.
[0038] The system 100 includes a sensor 1 which can detect the
analyte molecule, such as, e.g., a carbon nanotube (CNT) sensor. As
some examples for use as sensor 1, sensors useable as sensor 1 are
known and commercially available, such as, e.g., a sensor having
electrical properties that change with exposure to an analyte.
However, before this invention, the state of the art for fieldable
devices had not yet provided sensors both sufficiently sensitive
and versatile to detect a variety of important threat agents and
simultaneously discriminate or be insensitive to interferents which
could register an excessive number of false alarms, which problem
system 100 addresses, improving the specificity of a conventional
sensor when used as sensor 1 within system 100 compared to
stand-alone use of the same sensor.
[0039] In system 100, the sensor 1 is disposed within a chamber 2.
According to the invention, in system 100, the chamber 2 housing
the sensor 1 is divided into an upstream section 21, a section 22
near the sensor 1, and a downstream section 23. Particularly, the
system 100 is constructed to be sensitive to an analyte molecule
size, such as, e.g., considering the length of the analyte
molecule. For example, if the analyte molecule is a nerve gas,
nerve gases are in the length range of 0.727 to 1.320 nm, the
chamber 2 is divided to take into account that the analyte molecule
is in a length range of 0.727 to 1.320 nm. The system 100 is tuned
(such as, e.g., maximum length dimension-wise) to analyte molecule
size by providing a screen 10 that excludes all molecules bigger
than the size (such as, e.g., length) of the analyte molecule, and
by providing a screen 11 that permits to pass all molecules smaller
than the size of the analyte molecule. For example, if system 100
is being constructed for an analyte molecule that is a nerve gas,
the screen 10 is a screen that excludes all molecules with length
greater than 1.320 nm and the screen 11 is a screen that permits
passage of all molecules with length less than 0.727 nm.
[0040] Referring to FIG. 1, an initial sample is introduced via
inlet 3 into the system 100, and molecules smaller than the analyte
molecule make their way to downstream section 23, while molecules
bigger than the analyte molecule remain in upstream region 21. Only
molecules in the size range of the analyte molecule accumulate in
region 22 near the sensor 1. In the case of an analyte molecule
which is a nerve gas which is a range of about 0.727 to 1.320 nm, a
system 100 is constructed for use in a method in which the system
100 performs a reducing step that sorts from an initial sample
introduced via inlet 3 into the system 100 molecules which are
outside of a range of about 0.727 to 1.320 nm, requires molecules
which are bigger than 1.320 nm to remain in the upstream region 21,
and only permits molecules which are in the range of 0.0727 to
1.320 nm to accumulate in the region 22 near the sensor 1.
[0041] In system 100, for screens 10, 11, screens comprising carbon
nanotubes are preferred with screen 10 and screen 11 each being
constructed with respective dimensions. FIG. 1A shows a
cross-sectional view of a nanotube being used in screen 10. Each
carbon nanotube used in the screen 10 has a wall thickness, such as
wall thickness 10t is 0.26 nm which is the diameter of a carbon
atom. The outer radius 10R of the carbon nanotube in screen 10 is
shown. For practicing the invention, the inner diameter of a
nanotube is used. The inner diameter of a nanotube is the outer
diameter (such as twice the outer radius 10R) minus the wall
thickness (such as 10t), with some small adjustment made to reduce
the effect of van der Waal's forces or interactions that might
impede the motion of the sampled molecules through the nanotube
filter. An example of such a small adjustment is, e.g., to increase
the effective size of the analyte to be sensed, and which is used
in the selection of the inner diameter of the carbon nanotube
filters, by an amount sufficient to reduce the likelihood of wall
interactions impeding the movement of the analyte molecules in the
sample.
[0042] When a nanotube is being used within a screen that excludes
molecules of a maximum size, the nanotube should have an inner
diameter to exclude molecules bigger than the maximum size. When a
nanotube is being used within a screen that permits passage of
molecules of a minimum size, the nanotube should have an inner
diameter that permits passage of molecules below the minimum size.
It will be appreciated that the inner diameter of a nanotube being
used within a screen 10 or a screen 11 is not necessarily set
exactly equal to the molecule size which is to be excluded or
permitted passage, respectively. The precise requirements are
established by increasing the effective size of the analyte to be
sensed, and which is used in the selection of the inner diameter of
the carbon nanotube filters, by an amount sufficient to reduce the
likelihood of wall interactions impeding the movement of the
analyte molecules in the sample.
[0043] Much experimental evidence exists that molecules can easily
pass axially through nanotube structures when the molecule is
smaller than the internal diameter of the nanotube.
[0044] For example, one can be certain that a molecule that is 1.05
nm in diameter will not find its way easily through a carbon
nanotube that is exactly 1.05 nm in inner diameter; therefore, if
passage of molecules that are 1.05 nm in diameter is wanted, then
an inner diameter of the nanotube through which the 1.05 nm
diameter molecules are to pass should be slightly larger than 1.05
nm diameter being an example when constructing a screen to be used
to permit passage of molecules by an amount indicated above.
[0045] Screens 10, 11 (FIG. 1) preferably comprise more than one
nanotube. It will be appreciated that within one screen, all
nanotubes are not required to be of absolutely identical inner
diameter; a range of inner diameters is permissible for nanotubes
within one screen as long as they do not admit or pass molecules
that would engender excessive false alarms.
[0046] A screen 10, 11 optionally may comprise a compound filter
that comprises two or more carbon nanotube arrays in series, such
as two carbon nanotube arrays in series comprising a first carbon
nanotube array which differs from a second nanotube array as to
respective size screening. A compound filter may be used to sharpen
size sorting capability of a screen 10 or a screen 11.
[0047] An example for constructing system 100 is to use macro size
technology for the sensor 1, MEMS technology for the chamber 2, and
nanotechnology for the screens or filters 10, 11.
[0048] The inventive system 100 of FIG. 1 advantageously may be
used for sensing analyte molecules using the sensor 1 while
excluding interferent molecules from being sensed by the sensor 1,
of a size suited to the sizes of nanotube filters that can be
constructed.
[0049] The present invention provides an elegant solution
addressing the problem of false positives returned by a sensor
configured for an analyte (such as, e.g., sensor 1 in FIG. 1), such
as, e.g., inventive positioning of screens or filters (such as,
e.g., filters constructed of carbon nanotubes) relative to the
sensor 1 to limit the sensor 1 to being exposed to molecules within
a defined range of sizes, with molecules bigger than the defined
range being excluded from reaching the sensor by one filter 10, and
with molecules smaller than the defined range being caused to exit
(such as, e.g., pumped) through another, finer filter 11 before the
sensor 1 is operated.
[0050] The system 100 (FIG. 1) may be used, e.g., for sorting
different-sized molecules into three size categories including
relatively-big molecules, molecules of target-size (such as, e.g.,
molecules of a size of nerve gases), and relatively-small
molecules.
[0051] Referring to system 100, in which too-big molecules
accumulate in upstream section 21 and analyte molecules accumulate
near the sensor 1, after the sensor 1 has been applied to make a
measurement, if the system 100 is to be re-used on a new initial
sample, first the system 100 should be evacuated such as by
back-flushing.
[0052] In using an inventive system 100 (FIG. 1), the likelihood
that the sensor 1 is sensing an interferent rather than the analyte
molecule will be greatly reduced compared to using a stand-alone
sensor such as the sensor being used as sensor 1. However, in some
cases, there will still exist the possibility, albeit reduced, of a
false positive, i.e., that the sensor 1 in system 100 is responding
to presence of an interferent rather than presence of an analyte
molecule. Approaches for resolving whether an interferent is
present include, e.g., an assessment of the environment in which
the system 100 is operating (such as, e.g., a visual determination
by a human user that the sources of the interferent are not
present); an ambiguity resolver which is a second sensor dependent
on a different physical parameter. The computer-based ambiguity
resolver is preferred.
[0053] For example, in the course of operating an inventive
sensor-based system (such as, e.g., system 100, system 300 (FIGS.
3-4), etc.), a response of a sensor (such as, e.g., sensor 1 (FIG.
1), sensor S (FIGS. 3-4), etc.) is obtained through a step 500
(FIG. 5). In many cases necessarily there is ambiguity whether the
sensor response has been activated by an analyte or, rather, by an
interferent. Therefore, preferably the step 500 of obtaining the
sensor response is followed by an ambiguity-resolving step 502
(such as, e.g., an ambiguity-resolving step which comprises a
visual assessment of the environment in which the sensor is
operating; an ambiguity-resolving step which comprises operating a
computer-based system; an ambiguity-resolving step including
observations by a human user and prompting by a computer-based
system; an ambiguity-resolving step which includes querying by a
computer-based system having stored therein a library (such as,
e.g., a library of computer-readable data relating to analytes and
interferents) wherein the computer-based system wherein the
computer-based system queries at least one human user and receives
input from the human user; etc.
[0054] When the inventive system 100 (FIG. 1) is used to sort
molecules in an initial sample into too-big molecules, molecules of
target size, and too-small molecules, optionally, sorted molecules
of target-size may be subjected to further processing such as at
least one further chamber (not shown in FIG. 1) that is
specifically configured (such as through at least one additional
sensor which is different from sensor 1) to measure whether an
interferent is present or interferents are present.
[0055] The invention may also be used, e.g., in environmental
applications, first responder applications, hazardous materials
applications, chemical intelligence, law enforcement, etc.
[0056] The invention also may be applied to detecting and measuring
the concentration of toxic chemicals in water, such as, e.g., by
inventive systems and methods according to FIG. 7 (which is further
discussed in Inventive Example 5 below). Such an application to
water samples requires, in addition to adequate sensitivity,
chemical sensors that operate in water. The principles of the
invention as described for working with air samples are adapted
with minor modification to the case of water samples. The separator
and concentration steps work as well with water as air. In addition
to seeing large toxic molecules, the length separators see, instead
of a large number of molecules of nitrogen, oxygen, carbon dioxide,
and other atmospheric components, an equivalently large number of
water molecules. In the case of applying the invention in water,
the water flow is arranged so that after the selector/concentrator
cells have collected enhanced levels of analytes of interest, the
water is flushed out and replaced with air. Thus instead of an
integrated separator/concentrator cell having the chemical sensor
inside (as shown in FIG. 1), the sensor is in a separate cell that
always remains dry. Thus the modification consists of establishing
"plumbing" for two separate fluid flow paths. One is wet and sees
water and analytes. The second is dry and sees air and the
concentrated analytes. Additional valves are used. In this
application, the issue now is not false positives triggering
unnecessary defensive responses but rather the identification of
the potentially wide range of toxic chemicals present. Time is no
longer an issue because the water flows are continuous and no
immediate responsive action is required. Generally the detector in
this application does not have the severe limits on size, weight,
power, and speed that tactical warning or intelligence collection
missions impose. A second sensor, such as a mass spectrometer or
other sensor, may be used for ambiguity resolution.
[0057] The invention may be appreciated with reference to the
following examples, without the invention being limited
thereto.
Inventive Example 1
Detector Concept
[0058] By "sensor" herein we mean a device placed in a
concentration cell, such as a sensor which is a nanotube sensor. We
do not use the words "sensor" and "detector" interchangeably.
[0059] Referring to the accompanying FIGS. 1-1A, in system 100 a
valve V11 at the entry point is opened so that an entryway which is
upstream region 21 may receive the initial sample (which in this
example is a gaseous sample, such as a sample of air of unknown
composition). What ultimately is wanted is for the sensor 1 (such
as a carbon nanotube (CNT) bundle sensor) to perform its actual
sensing as would be done conventionally, but without being burdened
by encountering molecules which give false positives and are not
themselves wanted to be detected. However, at the same time, it is
wanted, e.g., for the sensor 1 to be able to detect if an analyte
molecule is present, even if present on the order of only parts per
billion or trillion.
[0060] In this inventive example, the analyte molecules are
considered and a size range is established for the analyte
molecules. The inventive preprocessing is to sort too-big molecules
and too-small molecules from the initial sample and only present
molecules in a size range for the analyte molecules to the sensor
1. Referring to the figure, the initial sample encounters a first
screen 10 (the left-most screen), said first screen 10 blocking
entrance into a chamber 22 in which the sensor 1 is disposed for
operation in due time. Preferably, the first screen 10 comprises a
plurality of nanotubes each of a diameter to prohibit passage of
too-big molecules. For example, in the case where nerve gases are
the analyte molecules for the sensor, the first screen excludes
molecules with length greater than 1.32 nm.
[0061] Preferably a further preprocessing is performed, by applying
a second screen 11 as shown in FIG. 1 (the right-most screen),
which is a screen through which too-small molecules may pass but
through which molecules within the size range established for
analyte molecules cannot pass. For example, in the case of nerve
gases, the screen 11 for permitting exit of too-small molecules
would permit molecules with length less than 0.927 nm to exit the
chamber 22 in which the sensor 1 is disposed. For example, methane
which is about 0.3 nm would exit. Preferably there is provided a
valve V12 and a pump P downstream of the screen 11 that permits
too-small molecules to exit, and the valve V12 is opened and the
pump P is operated to urge or require too-small molecules to exit
the chamber 22 in which is disposed the sensor 1.
[0062] For practicing the invention, it is preferable that the
range of sizes of analyte molecules to be sensed by a single sensor
1 be in a relatively narrow range, that is, that the analyte
molecules to be sensed by sensor 1 are relatively close in size.
For example, tabun, soman and cyclosarin which are nerve agents are
relatively close in size, and a single inventive system 100
comprising sensor 1 sensing tabun, soman and cyclosarin as analyte
molecules may be constructed.
Inventive Example 1A
[0063] Likewise to the manner that a molecular separator structure
was provided in Inventive Example 1 configured for screening-out
non-nerve gas molecules for use with a nerve gas sensor, it readily
can be appreciated that other respective molecular separator
structures likewise can be made with each molecular separator
structure configured for its own agent.
[0064] Preferably, the respective molecular separator structures
each tuned to a respective analyte molecule are placed in
parallel.
Inventive Example 1B
Packaging Various Collections of Functionalities to Accommodate
Different Domains of Applicability and User Requirements
[0065] 1. Multiple size ranges or continuous spectrum of size
measurement [0066] a. Each Range L.sub.1-L.sub.2 , is defined by
two CNT filters represented by a radius R.sub.1 and R.sub.2.
Multiple ranges measured simultaneously can be accommodated by
feeding each range of a common manifold. [0067] b. Each pair of CNT
filters in a parallel analysis manifold can be either: [0068] i.
Factory-installed [0069] ii. Field depot-installed [0070] iii.
User-installed [0071] 2. Form factor can be understood in terms of
current "smart" cell phones. [0072] a. Touch sensitive screen for
both function set selection, status readout, and output display.
[0073] b. Built in comm capability to enable receipt of local
status of forces information, weather models, adjacent detector
warnings with map location, and other advisory or backup data
[0074] c. Scrolling by page shifting touch [0075] d. Magnification
by two-finger motion or selection by one-finger touch. [0076] e.
Backlit screen [0077] f. Icons to reduce literacy requirement and
provide language transportability in combined military operations
[0078] g. Provision for downloading data to a central processor
that can be [0079] i. Separately worn or carried by user [0080] ii
Carried by other personnel [0081] iii. Manned or Unmanned Ground,
Sea or Air vehicle mounted [0082] iv. At a base prior to leaving on
mission [0083] h. Battery recharging cable. Power sources can be in
the above locations (i-iv) [0084] i. Incorporation of camera to
send ancillary data to central location for analysis to minimize
need to record information on surroundings. [0085] j. GPS function
handles all geolocation tasks [0086] k. Target size and weight
range of 3-16 oz. [0087] l. Direct downloading of software to field
unit for function updating or to add field applications as wanted
via a military version of an "iTunes" store [0088] m. Wireless,
packet switching, anti-jam, and/or burst communications [0089] 3.
Additional Features/capabilities can be incorporated: [0090] a.
Field changes of battery [0091] b. Clips and other attachment
devices for user or vehicular use [0092] c. Solar cell for battery
recharging [0093] d. Field or depot changeout of CNT filter pairs
[0094] e. Insertion of CNT sensors [0095] f. Voice input/output
[0096] Examples of user modes include, e.g., [0097] a. Military
missions where risk of attack must be considered. This implies need
for user stealth, small size, operation by user in protective
clothing [0098] b. Field intelligence collection where size and
weight requirements can be relaxed, with suitable/flexible
packaging [0099] c. Environmental area survey [0100] d.
Incorporation of detector into a user local area net [0101] e.
Commercial chemical plant HAZMAT safety [0102] 4. Architectures
[0103] a. Detector architecture such as the U.S. Department of
Defense Common CBRN Sensor Interface (CCSI"s specifications to
allows for families of compatible and interoperable devices) are
important [0104] b. A communications architecture to fit the
detector into an existing or specified communications network
[0105] c. An information architecture to define data formats and
with interfaces to support two-way transmission of e.g., data,
software, warning, etc. [0106] d. A logistics architecture to
include [0107] i. Device identification [0108] ii. Device location
[0109] iii. Device user or organization association [0110] iv.
Calibration of detector [0111] v. Status and maintenance condition
[0112] vi. Field diagnosis of malfunction [0113] vii. Field repair
such as resetting, recalibration, switching to built-in redundant
backup capability [0114] viii. Logging past locations, past
readings, malfunctions, change in operator or organizational
assignment [0115] ix. Incorporation of ancillary sensing functions
such as temperature, humidity, impact, sound level, light level
[0116] x. Flexible growth of detector with time to incorporate new
or improved physical devices, software-defined new functionalities,
replacement of damaged components [0117] 5. Seamlessly incorporate
the detector into systems planned or extant of the Army, Air Force,
Navy, intelligence community and other user communities including
but not limited to the Environmental Protection Agency and other
environmental monitoring organizations; industry associations such
as water supply, industrial occupation and industrial safety;
Department of Homeland Security, particularly at state, county, and
local levels; Federal Emergency Management Agency (FEMA);
Commercial Chemical plant safety; education and training groups for
university level (teaching and laboratory safety) and training
(industrial, military, law enforcement, first responders, disaster
response, etc.); transportation security needs such as passenger,
baggage or freight inspector; incorporate nuclear radiation sensor
for border control to protect against nuclear weapons and
radiological threats; etc.
Inventive Example 1C
[0118] Another inventive example is as follows. Call the section
between the first two valves, that contain two size filters L.sub.1
and L.sub.2 with a sensor in between a "cell" C.sub.12. If P is the
pump that draws the gas being measured, then the detector can be
denoted as --C.sub.13--P--.
[0119] There are other physical configurations possible that lead
to enhanced functionality. Suppose one wants to produce a
continuous "spectrum" of molecular lengths: [0120] 1-2, 2-3, 3-4, .
. . N--(N+1) between molecular length 1 and length N+1. These would
logically be in series, and denoted as: [0121]
--C.sub.12C.sub.23C.sub.34 . . . C.sub.N(N+1)--P-- Another useful
geometry would meet the military need to classify a detected agent
in a way that would assist in adopting appropriate protective
measures. For this there are three categories of agents of common
concern:
[0122] Blood agents: CK (cyanogen chloride; chemical formula CNCI)
and AC (hydrogen cyanide; chemical formula HCN). These are quite
small, of the order of 0.1-0.5 nm. To detect them one must select
that length range.
[0123] Another set of agents are the blister agents such as L
(lewisite; chemical formula C.sub.2H.sub.2As Cl.sub.3) are
intermediate in length. Lewisite is 0.9 nm while sulfur mustard
(C.sub.4H.sub.8Cl.sub.2S) is about 1 nm long. There are various
formulations of sulfur mustard, differing in being mixed with other
materials to enhance its effects under various conditions.
[0124] In this case, therefore, one could make a sensor that
distinguishes between the three classes, blood, blister, and nerve
agents by selecting three ranges: 0.4-0.5, 0.9-1.0. and 1.1-2.2 nm.
In this case they would be connected in parallel and each fed off a
common manifold, and each using the same suction pump.
##STR00001##
There can be combinations of serial and parallel cell arrangements
chosen and fabricated to fit particular user needs. For example,
since the size range of nerve agents is so large, one may want to
divide it more finely, breaking down the 1.1-2.2 nm range into a
continuous length spectrum of four or five sub-pieces.
[0125] Another variation is to use either a second suction pump or
the same suction pump with a more complex set of valves and
"piping" to feed any of the contents of any of the concentration
chambers between the CNT length filters into a separate section C*
based on other molecular parameters and using a sensor or sensors
responsive to other physical properties such as dipole moment,
chemical reactivity reactivity, etc. (C* may be configured in
series and parallel, not shown.) This could be drawn as:
##STR00002##
(For simplicity, without showing all valves).
[0126] The electronics may include other functions and be
structured with an open architecture to allow the device to become
a subsystem of a larger system or to provide a basis for adding on
other subsystems to it.
Inventive Example 2
Operation of Flow Controller
[0127] A system 300 (FIG. 3) that receives air is constructed,
comprising a pump (P) to draw in air containing the analyte or
analytes. The system 300 further comprises at least one length
separator 301 that selects molecules in a selected size range. The
system 300 further comprises a concentrator 311 integrated with
each separator 301, wherein concentrator 311 and length separator
301 may be the same component. The system 300 further comprises a
sensor (S) integrated with each separator 301, the sensor (S) being
a suitable sensor to detect the target analyte or analytes. The
system 300 also comprises an analyzer 300A to interpret the sensor
outputs from each separator 301. The system 300 further comprises
an interactive interrogator 305 which is a computer-implemented
system or device (such as, e.g., an interactive interrogator that
receives at least one of: user inputs from a human user or users
and/or receives data from a remote system and/or receives or
contains a library in a computer-readable form of analytes and
possible interferents). Also the system 300 comprises a flow
controller (FC) to manage operation of the separator, concentrator
311, ambiguity resolver 303 if any, and to manage backwash
operations including operation of the valves VEN, V11, V12, VN1,
VN2, V3, V4, V5, VEX and the pump (P). The system 300 further
comprises a vaporizer 302 to convert liquid-phase analytes in an
airflow to vapor phase. Optionally the system 300 comprises an
ambiguity resolver 303.
[0128] In FIGS. 3-4, N cells 33 are in parallel of which an example
of a cell 33 is shown in FIG. 3A.
[0129] Referring to FIG. 3, a pump (P) draws in a fluid to be
sampled. The pump (P) has a volumetric capacity of R vol/sec. The
system 300 comprises an entrance valve VEN and an exit valve VEX.
Valves VEN and VEX are connected to the flow controller (FC). By
varying the size, weight, and power consumption of the pump (P)
used in system 300, the size, weight, power sensitivity, and
measurement time of the system 300 can be varied.
[0130] Referring to FIGS. 3-4, one or more separators 33 are
connected in parallel to an entrance manifold M1. In FIG. 4, the
number of separators 33 illustrated is merely representational of
"N", where N is an integer 1 or greater. A separator 33 may also be
referred to as a separator cell 33.
[0131] A separator 33 has an entrance face which consists of an
array of roughly parallel nanotubes open at both ends and oriented
in the direction of the flow of the sampled fluid, each of roughly
the same inner diameter and roughly the same length, thus
constituting a molecule filter. The inner diameter D1 of each
entrance face (i.e., the first) nanotube filter is equal to the
minimum diameter of molecules to be excluded from said separator
33. D1 is chosen to be slightly larger than that of the diameter of
the analyte molecule or molecules. "Diameter of the molecule" means
the maximum diameter swept out by a molecule rotating about an
arbitrary axis through the center of mass of the molecule subject
to normal thermal collisions before encountering the first nanotube
filter.
[0132] The exit face of the separator 33 consists of an array of
roughly parallel nanotubes open at both ends and oriented in the
direction of the flow of the sampled fluid, each of roughly the
same inner diameter and roughly the same length thus constituting a
second molecule filter. The inner diameter D2 of the exit face
nanotubes are such that D2 equals the maximum diameter of the
molecules not to be retained in said separator 33 but instead
allowed to exit said separator 33.
[0133] The separator cell 33 (FIGS. 3-4) thus selects molecules
whose maximum diameter D falls within the range D1>D>D2. On
one of the walls of the cell 33 is a sensor (S) that produces an
electrical signal that is a function of the concentration of the
analyte molecule or molecules in the sampled fluid drawn through by
the pump (P). Such electrical connections as required are passed
through a wall of a chamber enclosing the sensor (S), to the
outside, and are available for connection to the analyzer 300A.
[0134] A valve V11 at the entrance of the first separator cell of
the separator cells 33 and a valve V12 at the exit of the first
separator cell of the separator cells 33 is then closed by a flow
controller (FC) when the analyzer 300A determines that the
analyte's or analytes' concentration measurement is complete, or
after a maximum pumping time set by the user. When there is more
than one separator cell 33, this step is performed for each of the
cells 33 at a time determined by the analyzer 300A, or after a
maximum pumping time set by the user.
[0135] In order for the fluid sample containing the analyte or
analytes to be removed from the cell 33 when commanded by the user
at the conclusion of the measurement in preparation for a
subsequent fluid sample to be introduced into the cell, valves V11,
V12 and VEN are opened, VEX is closed, and the cell 33 is cleansed
of the analyte or analytes through back-flushing. Table 1 shows the
position of each of the valves in the system 300 in the shut down
state, during the measurement time, during operation of the
ambiguity resolver 303, and during the backwash operation.
TABLE-US-00001 TABLE 1 Valves Shut- Ambiguity Resolution and down
Measurement state (illustration Back-flush Pump state operation for
Cell 1 only) operation VEN closed open closed open V11 closed open
closed open V12 closed open open open VN1 closed open closed open
VN2 closed open closed open V3 closed open close open V4 closed
closed open open V5 closed closed open open VEX closed open closed
closed Pump off on (inflow) on (inflow) on (outflow)
For the system 300 in FIGS. 3-4, using at least one cell 33 (FIG.
3A), Table 1 shows whether each of valves VEN, V11, V12, VN1, VN2,
V3, V4, V5, VEX is closed or open and whether the pump (P) is off
or on for different respective states and operations including a
shut-down state, a measurement operation, an ambiguity resolution
state and a back-flush operation. In Table 1, the column for
Ambiguity Resolution state is an illustration only for one cell
33.
[0136] Each separator cell 33 acts as a concentrator to increase
the sensitivity of the system 300. For a separator cell 33 having a
volume V, the pump (P) will fill this volume V in a time T=V/R
where R is capacity of the pump (P). For a configuration having N
cells 33 in parallel, each cell 33 the same size, the time to fill
all of the cells 33 is T=NV/R. Further suppose that the desired
sensitivity of the measurement of each cell 33 is a concentration
of molecules of c/unit volume but the maximum sensitivity of the
sensor (S) is only s molecules/unit volume. It will be necessary to
fill the cell 33 volume repeatedly to achieve a concentration ratio
CR that is s/c times greater, each time retaining the analyte or
analytes until the cell 33 volume has sufficiently concentrated the
analyte or analytes such that the sensor (S) is able to register
their presence. Therefore
TR=V.times.N.times.s/c
in which operational requirements of the system 300 will set T, c,
and N. Therefore the pump capacity R is set by the cell volume V
and the maximum sensitivity, s, of the sensor (S).
[0137] The sensor (S) in an integrated sensor/concentrator cell 33
operates in the following manner. A sensor (S) has a resistance
that is altered by the attachment of an analyte molecule to a
surface of the sensor (S) or to an internal structure of the sensor
(S) forming one wall of the separator/concentrator cell 33. At
least two electrical connections including the two ends of a
resistive element extend through a wall of the cell 33 and connect
to the analyzer 300A.
[0138] The analyzer 300A consists of an electronic data processor.
The analyzer 300A comprises a voltage source that applies a voltage
to each sensor (S). Each respective sensor (S) in each of the cells
33 need not be identical in material or construction to another
sensor (S). The analyzer 300A also has a voltage measuring
capability that records the change in resistance of the sensor (S)
with exposure to the analyte or analytes in the cell 33. The
analyzer 300A comprises a clock that provides a time base against
which to measure resistance changes and based on which measurements
and actions performed by the system 300 are time-tagged. The
analyzer 300A comprises an algorithm that recognizes resistance
changes in the sensor (S) as a function of time, interprets this
change in terms of chemical concentration, and determines a
response of sensor (S) in accordance with procedures specified by
the user through the interactive interrogator 305. The analyzer
300A comprises a display, such as a display that provides three
colored green/yellow/ red lights viewable by a user for each of the
respective cells 33 in which green indicates that no analyte or
analytes above a user-specified alerting threshold are present,
yellow indicates that some analyte or analytes are present above a
user-specified threshold, and red indicates that a user-specified
dangerous level of analyte or analytes is present. The analyzer
300A comprises a logic element that generates required signals for
the flow controller (FC) to open and close valves. The analyzer
300A comprises logic elements based on which the system 300
provides more detailed information to the user through a display
that is part of the interactive interrogator 305 and is commanded
by the user. The analyzer 300A comprises a logic element that
communicates such information as the user may have indicated to be
supplied to a communications device for transmission to a higher
level sensor/response system of which system 300 is a subsystem or
component.
[0139] The system 300 further comprises an interactive interrogator
305 which receives commands of a user. Interactive interrogator 305
provides environmental information to the user and analyzer 300A to
determine a response, or range of responses, to be provided to the
user through the display. The interactive interrogator 305 may
comprise, e.g., a receiver for GPS coordinates; a communication
capability for establishing connection with a wind sensor; a
digital camera; etc. Examples of environmental information that the
interactive interrogator 305 provides (such as providing in
computer-readable form) to the analyzer 300A are, e.g., GPS
coordinates of the sensor (S) at the time a measurement is made;
wind speed and direction (provided either by user measurement or
estimate or from a wind sensor or database); environmental
information relating to presence of possible chemical interferent
sources needed by the analyzer 300A to make correct deductions from
measurements taken by sensor (S) and downloaded to the analyzer
300A (which environmental information relating to presence of
possible chemical interferent sources may be downloaded to the
analyzer 300A from a remote database); a library of chemical
compounds consisting of precursors or products (such as, e.g., a
library of chemical compounds consisting of precursors or products
derived from actual activities observed by the user to be present);
etc. In addition, a digital camera may optionally be used to
produce images, such as, e.g., images reviewable by a remote user
at a different location away from the sensor (S) to evaluate the
interferent potential presented by the environment in the vicinity
of the sensor (S).
[0140] In the system 300, the flow controller (FC) opens and closes
valves, controls the flows into and out of the single or multiple
cells 33, controls the operation of vaporizer 302, controls the
flow to an optional ambiguity resolver 303, and controls back-flush
of the system 300 following a measurement by sensor (S). The flow
controller (FC) receives status information from the analyzer 300A
when a cell 33 has completed a measurement, when the at least one
cell 33 is to be emptied in preparation for a next measurement
sample, and when the user requests information from the ambiguity
resolver 303.
[0141] Under the temperature and pressure conditions when the
measurement or measurements are made by the sensor (S), analytes
can be in either a vapor phase or can be small droplets of liquid
phase. To be certain that such analytes that are liquid droplets as
may be present are completely measured, on entry into the system
300 they pass through a vaporizer 302 that emits electrical, laser,
thermal energy or other means sufficient to vaporize liquid phase
analytes if any.
Inventive Example 2A
Ambiguity Resolution
[0142] Referring to Example 2 and system 300, it is possible that
upon completion of an analyte's or analytes' concentration
measurement in a cell 33, there maybe ambiguity as to whether the
separated vapor is an analyte or interferent. In such a case of a
potential false positive, optionally the analyzer 300A communicates
this status onwards, such as, e.g., communicating this status to
the user for handling or the status is directly presented by the
flow controller (FC) to an ambiguity resolver 303. In the case in
which the status is directly presented by the flow controller (FC)
to ambiguity resolver 303, the exit valve VN2 on the cell or cells
33 that are registering are sequentially opened. Valve V3 is closed
and valves V4 and V5 are opened and the concentrated samples
contained therein are presented to a follow-up sensor (not shown in
FIGS. 3-4) which is not sensor (S), which follow-up sensor is
capable of making a further determination based on a different
physical property of the molecule or molecules than was sensed by
sensor (S), with information relating to the different physical
property being contained in the library.
[0143] This example a system 300 which includes a length separator
301 further includes an ambiguity resolver 303 which is a
hardware-based ambiguity resolver consisting of a sensor responsive
to a physical characteristic (which is not a length characteristic)
of an analyte or analytes.
Inventive Example 3
Reducing False Positives in Sensing Chemical Warfare Agents
(CWA)
[0144] A preliminary spreadsheet was prepared for over 1700
compounds including chemical warfare agents and the rest chemicals
derived from an analysis of the list of DoD "interferents," e.g.
burning rubber and the chemical compounds derived from those
processes. The DoD interferents are illustrative of combat
operations and various chemicals such as arising from vehicles and
housekeeping materials typically found in closed spaces.
Information such as chemical names, structural formula, molecular
weight, melting point, boiling point (to know what are gases at
standard temperature and pressure), and vapor pressure was
compiled.
[0145] Using molecular modeling software, maximum diameters of
circumscribing spheres were calculated and tabulated.
[0146] From the preliminary spreadsheet, the false positive
situation, namely, potential vapor phase false positives could be
seen using molecular length as the primary selection criterion.
Based simply on molecular length, there were 51 possible
interferents.
Inventive Example 3A
Ambiguity Resolution by Means of a Second Physical Sensor
[0147] Although other alternative approaches for reducing the
number of false positives in Example 3 may be possible, the
preferred approach is to use a second selection criterion to rule
out the possibility of a false positive. This has the advantage of
not having to rely on local circumstances, local judgments, and
local expertise.
[0148] An example of a second selection criterion is molecular
weight, such as by using in series with the CNT length selector, a
mass spectrometer.
[0149] Table 2 is based on a length-first selection dividing the
length range in the preliminary spreadsheet from 0.63 nm to 1.39 nm
into two ranges, 0.63 to 0.97 nm and 1.04 nm to 1.39 nm. One then
brackets the molecular weight of the chemical agents in each of
these length ranges from smallest to largest and looks to see if
any of the interferents still fall into the joint selection range.
The results for this example are:
TABLE-US-00002 TABLE 2 TOTAL NO. OF NO. OF NO. OF LENGTH LENGTHS
LENGTH MOLECULAR CHEMICAL INTERFERENTS INTERFERENTS RANGE SELECTED
RANGE WEIGHT AGENTS IN IN RANGE (LENGTH PLUS (NM) (NM) (NM) RANGE
RANGE (LENGTH ONLY) MW) 1 0.63-0.97 0.34 140-180 5 32 2 2 1.04-1.39
0.35 198-239 5 19 0
Examples 3-3A illustrate how to select detector parameters based on
the problem being addressed.
[0150] Upon applying the joint selection criteria of Examples 3-3A,
only two residual interferents got through the joint selection
criteria, 1,2 dichlorobenzene and isopharone. Therefore through
Examples 3-3A, the number of interferents has been substantially
reduced from the beginning number.
Inventive Example 4B
Application of Library of Analytes and Interferents
[0151] For constructing a table with rows that include at least one
analyte and include interferents for that analyte, the following
columns may be used: interferent source, chemical derived therefrom
(from these two columns, a local user can indicate what is not
present); molecular weight; melting point, boiling point (these
columns are used to tell solid from vapor from liquid); vapor
pressure (possibly to rule out a compound); maximum diameter, of
which the columns for interferent source and maximum diameter are
considered most important.
[0152] In FIG. 2, the rows have been sorted by maximum diameter and
are shown in increasing order of maximum diameter. Of the columns
in FIG. 2, interferent source and maximum diameter are considered
most useful for designing systems, methods, devices and apparatuses
according to the invention.
Inventive Example 5
Detecting Analytes in Water Samples
[0153] Referring to FIG. 7, the water being sampled is drawn
continuously under suction produced by pump P1 through the
selector/concentrator cells S/C. For this to occur, valve VEN, V11
and V12 are open, as well as the corresponding valves on the other
selector/concentrator cells selected for use. In FIG. 7 only two
S/C are shown for simplicity, S/C1 and S/C2 so that V21 and V22 are
open also.
[0154] The water flow (FIG. 7) continues as with the air sampling
case. Each selector/concentrator cell has two molecular-length
defining pairs of CNT filters, one at the entrance and one at the
exit of the cell as shown in FIG. 1. In this way molecules of a
specified size range are captured and retained.
[0155] The sampled water first enters manifold M1 (FIG. 7) from
which it flows to the active selector/concentrator cells and the
outflow from each of the selector/concentrator cells is collected
in manifold M2 prior to exiting the apparatus through valve VEX
which is open. The only feature different from the air case is that
bodies of water will have a variety of types and sizes of
particulate matter. These must be excluded lest they clog the CNT
filters and so a conventional particulate filter is shown after
entrance valve VEN and before manifold M1 (FIG. 7). The pore size
of this conventional filter is chosen based on the size of the
particulates present in the sampled water. Typically it will be of
the order of 1 micron.
[0156] Valves V13 and V14 (FIG. 7) are closed, as well as the
corresponding valves for S/C2 which is similarly constructed but
with CNT filters selected to be of a size that a different desired
molecular length range is defined. In FIG. 7 as shown in FIG. 4
there is no limit to the number of selector/concentrator cells that
may be operated in parallel beyond the ultimate practical limits on
size, cost, and power.
[0157] As with air sampling, pump P1 (FIG. 7) is operated for a
time set by the user, that time being selected to increase the
sensitivity of the apparatus such that it will be able to register
toxic materials at levels deemed harmful.
[0158] When the pumping time has been reached, pump P1 is closed
down as well as valves V11 and V21 (in this example of two
selector/concentrator cells in use.) The apparatus is now filled
with water in what might be called the "water loop." The water in
the selector/concentrator cells contain, in addition, concentrated
analytes whose molecular size falls within the CNT filter-defined
length ranges. All other parts of the apparatus are dry. At this
point the analytes have not been presented to a sensor and thus
have registered no signal, for the reason that no suitable sensors
capable of operating in an aqueous environment are available.
[0159] The next step is to drain out the water from the
selector/concentrator cells. This is done by restarting the pump P1
and opening valves V13 and V23. This allows the water to be pulled
out of the water loop of the apparatus and replaced by air that
flows into each active selector/concentrator cell through manifold
M3. When this is completed, V12 and V13, are closed and valve V14
is opened, valve V15 remaining closed, and the corresponding valves
on S/C2 operated similarly. This results in the air enriched with
analytes extracted from the water sample in S/C1 being exposed to
sensor S1, and similarly for S2. Because the partial pressure of
the analytes in S/C1 is greater than that in S1, which is devoid of
analytes, mixing will occur and S1 (FIG. 7) will be able to respond
with the same kind of electrical signal as in the case of the air
sampled flow in FIG. 4. The speed of this mixing could be increased
by heating S/C1 to increase the pressure of the gases therein
should this be deemed important for a particular sampling
application. This part of the apparatus can be called the "air
loop."
[0160] When the measurement of the analyte concentrations in the
selector/concentrator cells is completed, the apparatus must be
cleared to prepare it for the next water sample. This sample could
be in a different field location, or the same location at some
later time, or for a next sample to be measured in a central
measurement laboratory undertaking this kind of analysis as an
internal service or as a commercial service.
[0161] At this point there are two ways of proceeding. If the
measurement is deemed to be unambiguous, valves V13, V15, V3, and
VEX are opened, with V4 and V5 remaining closed, and pump P2 pulls
the air into manifold M4 and out of the apparatus and the
subsequent flow cleans all the analyte in S/C1 and S1 from the air
loop. This process is repeated sequentially for all the other
selector/concentrator cells employed.
[0162] If, however, there is an ambiguity in the measurement from
S1, V3 is closed and valves V4 and V5 opened and pump P2 presents
the ambiguity sensor with the analyte or analytes from S1. This
process is repeated for all the other selector/concentrator cells
employed requiring ambiguity resolution.
[0163] In addition to back-flushing the air loop, the water loop
must be back-flushed. This is done by opening VEN, V11, V12, and
the corresponding valves on S/C2 and all other active
selector/concentrator cells. Pump P1 is then reversed and it pushes
sample water through the water loop. The CNT filters do not impede
the cleaning of each selector/concentrator cell since the analyte
molecules can flow back through the CNT filters past which they
entered.
[0164] At this point all valves are returned to their initial
position and the apparatus is ready for the next sample.
[0165] The following Table 2 summarizes the valve positions and
pump operation for the several states of the apparatus. The
information is, for simplicity, shown for the case of only one
active selector concentrator dell, S/C1:
TABLE-US-00003 TABLE 2 VALVES AND SHUT-DOWN WATER DRAIN SEL/ MOVE
ANALYTES TO AMBIGUITY BACK-FLUSH BACK-FLUSH PUMPS STATE SAMPLING
CONC CELL AIR LOOP SENSOR RESOLUTION AIR LOOP WATER LOOP VEN closed
open closed closed closed closed open V11 closed open closed closed
closed closed open V12 closed open open closed closed closed open
V13 closed closed open open closed open closed V14 closed closed
closed open closed closed closed V15 closed closed closed closed
open open closed V3 closed closed closed open closed open closed V4
closed closed closed closed open open closed V5 closed closed
closed closed open open closed VEX closed closed closed closed
closed open closed P1 off on(suction) on(suction) on(suction) off
off on(pressure) P2 off off off off on(suction) on(suction) off
[0166] While the invention has been described in terms of a
preferred embodiment, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the appended claims.
* * * * *